1. Field of the Invention
The present invention relates to a sheet conveying device for use in an image forming apparatus such as a copying machine, a printer, a facsimile machine, a multi-functional image forming apparatus, or other similar image forming apparatuses.
2. Discussion of the Background
A background sheet conveying device, which conveys a sheet in a predetermined direction while pinching the sheet between a drive roller and a driven roller which is press-contacted against the drive roller, has been proposed. With regard to a roller support mechanism that press-contacts the driven roller against the drive roller in the above-described background sheet conveying device, for example, Japanese Laid-open patent publication No. 63-66583 describes a roller support mechanism that uses a plate spring functioning as a roller support member. The plate spring rotatably supports a driven roller and exerts a bias force on the driven roller to be press-contacted against a drive roller. Japanese Laid-open patent publication No. 9-188449 also describes a roller support mechanism that uses a plate spring to bias a driven roller against a drive roller.
FIG. 1 is a perspective view of a background sheet conveying device including a roller support mechanism using a plate spring. In the background sheet conveying device of FIG. 1, a pair of sheet conveying rollers 123 include a drive roller 130 (illustrated by dotted lines) and a driven roller 131. A plate spring 132 rotatably supports the driven roller 131. Specifically, the driven roller 131 is supported by a pair of support arms 134 which are provided on one end part 132b of the plate spring 132. Two through holes 138 are formed in the middle part of the plate spring 132 at a predetermined distance apart. The background sheet conveying device of FIG. 1 further includes a guide plate 109. The guide plate 109 includes a support hole 136 and two protrusions 137 on the surface of the guide plate 109 at a predetermined distance apart. The plate spring 132 is fixed to the guide plate 109 by inserting the other end part 132a and a stepped bent part 133 of the plate spring 132 into the support hole 136 and by engaging the two protrusions 137 that are provided on the guide plate 109 in the two through holes 138 in the plate spring 132.
FIG. 2 is a perspective view of another background sheet conveying device including a roller support mechanism using a plate spring. In the background sheet conveying device of FIG. 2, a plate spring 102 rotatably supports a driven roller 101 on one end part 102a of the plate spring 102 and biases the driven roller 101 against a drive roller 103. The plate spring 102 is fixed to a plate-shaped holding member (not shown) that holds the plate spring 102 by press-fitting a protrusion 104a that is provided on the holding member into a hole (not shown) that is formed at the other end part 102b of the plate spring 102.
FIG. 3 is a perspective view of the background sheet conveying device of FIG. 2 according to an alternative example. In the background sheet conveying device of FIG. 3, the plate spring 102 is fixed to a plate-shaped holding member (not shown) that holds the plate spring 102 by securing the other end part 102b of the plate spring 102 to the holding member by a screw 105.
In the background sheet conveying device of FIG. 1, when the plate spring 132 is attached to the guide plate 109, the position of the driven roller 131 relative to the drive roller 130 is regulated by the two protrusions 137. However, because the distance between the two protrusions 137 is relatively small, it may be difficult to insure the accuracy of the position of the driven roller 131 relative to the drive roller 130.
Further, as described above, in the background sheet conveying device of FIGS. 2 and 3, the plate spring 102 is fixed to the plate-shaped holding member by press-fitting the protrusion 104a on the holding member into the hole of the plate spring 102 by use of a jig (not shown), and by securing the other end part 102b of the plate spring 102 to the holding member by the screw 105. In these background sheet conveying devices, it may be difficult to control the accuracy of the position of the driven roller 101 relative to the drive roller 103 and to control the pressure of fixing the plate spring 102 to the holding member. Further, in the case of fixing the plate spring 102 to the holding member by the screw 105, the plate spring 102 may be bent around the screw 105 due to torque.
In the above-described sheet conveying devices, when a driven roller is not in proper alignment with a drive roller, specifically, when the shaft of the driven roller is not in parallel with the shaft of the drive roller, a sheet may be skewed in a sheet conveying path.